The present invention relates to an arrangement for removing dust from turning bars in folders for printing machines and more particularly, to a dust removal arrangement in which one or more suction chambers are provided in the area of one of the two lateral edges of a paper web and discharge electrodes are arranged at the paper inlet.
Folders used, for example, for printing machines have turning bars by which the moving direction of the paper webs passing through is reversed. By virtue of ventilated turning bars, the cutting dust carried along at the cutting edges is repelled an deposited both by the blowing air of the turning bar and the centripetal acceleration. As a result, dust formation impairs the operation of the whole folder and, up to now, has made it necessary to clean the folder mechanically at certain time intervals.
It is an object of the present invention to provide an arrangement for removing dust which occurs during cutting widths of material in printing machines which makes mechanical cleaning unnecessary.
The foregoing object of the present invention has been achieved by providing an arrangement in which, at least in the area of one of two lateral edges of the paper web, one or more chambers are provided, each extending in the same direction as the turning bar, and one or more individually arranged one behind the other in a curved manner, in the moving direction of the paper, around a portion of the turning bar, with discharge electrodes arranged at the paper inlet in the area in front of a first suction chamber and at the paper outlet in the area behind the last suction chamber on the side of the paper web not having the turning bar.
According to a presently preferred embodiment of the present invention, at least in the area of one of the lateral edges of the paper web at which a dust removal is to take place, the turning bar, as viewed in cross-section, has a semicircular portion surrounded by several suction chambers. The suction chambers may also be arranged, however, so that, in respective pairs, they cover the two lateral edges of the paper web. When creation of a large amount of dust is expected, suction chambers may also be arranged over the entire width of the paper web.
A high d.c. voltage is applied to discharge electrodes arranged at the paper inlet and at the paper outlet in which case the turning bar, preferably with respect to this d.c. voltage, may be grounded or insulated by an appropriately sized bleeder resistor. Because of the low dust formation, the danger of an explosion caused by dust is thereby reduced.
As a result of the semicircular arrangement of the suction chambers, as viewed in cross-section, the dust particles which are thrown off tangentially during rotation around the turning bar are sucked away. The suction effect can be further improved when the turning bar is rigid and hollow and, at least in the angle of wrap of the paper web, has a perforation to which compressed gas or compressed air is supplied by way of the interior of the hollow turning bar. This compressed gas or compressed air is then sucked off by the suction chambers. This arrangement has the advantage that an air cushion is generated on the turning bar over which the paper web "floats" when it moves over the turning bar. In addition, the rotation of the paper web around the turning bar is improved because it exercises a suction effect on the paper web, while the air cushion reduces the frictional forces. The high air current formed at the edges of the paper web promotes the suction effect during the dust removal.
A further feature of the present invention includes the space between the paper inlet and the paper outlet being constructed as a suction chamber. As a result, the dust particles occurring between the webs and the dust particles deposited on the rear side of the turning bar because of turbulence are also sucked off.
The suction chambers which surround the turning bar in a semicircular arrangement, as viewed in cross-section, and which are connected with a suction device, such as a pump, at their sides facing the paper web or the turning bar, are bounded, at their sides facing the paper web or the turning bar, by a plurality of roller-shaped boundary elements which are arranged at such distances from one another that sufficient space remains between them for the passage of the sucked-off dust particles. Roller-shaped boundary elements have proved to be particularly effective for this purpose because they offer fewer points of attachment for deposition of the dust particles to be sucked off. The suction chamber disposed in the space between the paper inlet and the paper outlet, at its side facing the turning bar, may be bounded at least partially by the roller-shaped boundary elements.